Effect of oxidizer in the synthesis of NiO anchored nanostructure nickel molybdate for sodium-ion battery
Sodium-ion batteries are an excellent candidate to meet the challenge of grid-level storage because of the abundance and low cost of sodium resources. It is crucial to identify suitable anode material for such batteries in order to replace the current technology involving metallic sodium- or carbon-based anodes. Anodes of metal-ion batteries determine key characteristics, such as safety issues and cyclability. Nickel molybdate (NiMoO4) is an alternative candidate material for anode applications, possessing a number of useful characteristics. In this work, we have produced the phase by solution combustion synthesis. We have investigated the influence of oxidant (NH4NO3) concentration and optimised it to produce desirable material characteristics. The oxidant has a central role in the synthesis, being able to influence the properties of NiMoO4including the electrochemical performance. At a low concentration of oxidiser (NH4NO3) the product obtained is partly crystalline and contains carbonaceous impurities while at a higher concentration of oxidiser, the reaction is incomplete forming secondary phases. The optimised fuel-to-oxidiser ratio is found to be around 1:1 whereby the oxidant is able to interact and chelate metal cations. This optimised material produces a high initial discharge capacity of NiMoO4vs. Na of 550 mAh g−1at a current density of 0.05 A g−1. However, the reversible capacity is found to be 245 mAh g−1but resulted in good capacity retention of 82% after 50 cycles and higher rate capability performance. This anode material is comparable to the capacity and outperforms by the voltage of classical carbon anodes used in sodium-ion battery. In the case of material produced with the lowest and highest concentrations, capacity retention is 45% and 75%, respectively. The electrochemical intercalation of Na ions into nickel molybdate produces a new type of intercalation compound (Na2MoO3) and this is discussed. These results provide insight regarding a versatile methodology based on solution combustion synthesis and an alternative insertion-type anode to metallic sodium or carbon.